Don't call stat() just to determine symbolic lengths

The new bftw_cached_stat() helper gets us stat info if we already have
it, but doesn't call stat() if we don't.  In that case we just take a
guess for the initial length to readlinkat().  This lets us avoid stat()
entirely in many cases for -lname and -printf %l.

5 files changed, 30 insertions, 11 deletions

diff --git a/bftw.c b/bftw.c
index ff4797d..1296360 100644
--- a/bftw.c
+++ b/bftw.c
@@ -886,6 +886,14 @@ const struct bfs_stat *bftw_stat(const struct BFTW *ftwbuf, enum bfs_stat_flag f
 	return ret;
 }
 
+const struct bfs_stat *bftw_cached_stat(const struct BFTW *ftwbuf, enum bfs_stat_flag flags) {
+	if (flags & BFS_STAT_NOFOLLOW) {
+		return ftwbuf->lstat_cache.buf;
+	} else {
+		return ftwbuf->stat_cache.buf;
+	}
+}
+
 enum bftw_type bftw_type(const struct BFTW *ftwbuf, enum bfs_stat_flag flags) {
 	if (ftwbuf->stat_flags & BFS_STAT_NOFOLLOW) {
 		if ((flags & BFS_STAT_NOFOLLOW) || ftwbuf->type != BFTW_LNK) {
diff --git a/bftw.h b/bftw.h
index 0a4f2aa..2198b52 100644
--- a/bftw.h
+++ b/bftw.h
@@ -131,6 +131,19 @@ struct BFTW {
 const struct bfs_stat *bftw_stat(const struct BFTW *ftwbuf, enum bfs_stat_flag flags);
 
 /**
+ * Get bfs_stat() info for a file encountered during bftw(), if it has already
+ * been cached.
+ *
+ * @param ftwbuf
+ *         bftw() data for the file to stat.
+ * @param flags
+ *         flags for bfs_stat().  Pass ftwbuf->stat_flags for the default flags.
+ * @return
+ *         A pointer to a bfs_stat() buffer, or NULL if no stat info is cached.
+ */
+const struct bfs_stat *bftw_cached_stat(const struct BFTW *ftwbuf, enum bfs_stat_flag flags);
+
+/**
  * Get the type of a file encountered during bftw(), with flags controlling
  * whether to follow links.  This function will avoid calling bfs_stat() if
  * possible.
diff --git a/color.c b/color.c
index 11684ef..4b70e19 100644
--- a/color.c
+++ b/color.c
@@ -841,11 +841,8 @@ static int print_path(CFILE *cfile, const struct BFTW *ftwbuf) {
 static int print_link_target(CFILE *cfile, const struct BFTW *ftwbuf) {
 	int ret = -1;
 
-	size_t len = 0;
-	const struct bfs_stat *statbuf = bftw_stat(ftwbuf, BFS_STAT_NOFOLLOW);
-	if (statbuf) {
-		len = statbuf->size;
-	}
+	const struct bfs_stat *statbuf = bftw_cached_stat(ftwbuf, BFS_STAT_NOFOLLOW);
+	size_t len = statbuf ? statbuf->size : 0;
 
 	char *target = xreadlinkat(ftwbuf->at_fd, ftwbuf->at_path, len);
 	if (!target) {
diff --git a/eval.c b/eval.c
index f8b9a6d..b50efd7 100644
--- a/eval.c
+++ b/eval.c
@@ -484,12 +484,10 @@ bool eval_lname(const struct expr *expr, struct eval_state *state) {
 		goto done;
 	}
 
-	const struct bfs_stat *statbuf = eval_stat(state);
-	if (!statbuf) {
-		goto done;
-	}
+	const struct bfs_stat *statbuf = bftw_cached_stat(ftwbuf, BFS_STAT_NOFOLLOW);
+	size_t len = statbuf ? statbuf->size : 0;
 
-	name = xreadlinkat(ftwbuf->at_fd, ftwbuf->at_path, statbuf->size);
+	name = xreadlinkat(ftwbuf->at_fd, ftwbuf->at_path, len);
 	if (!name) {
 		eval_report_error(state);
 		goto done;
diff --git a/printf.c b/printf.c
index b9149f3..6eb59dd 100644
--- a/printf.c
+++ b/printf.c
@@ -310,7 +310,10 @@ static int bfs_printf_l(FILE *file, const struct bfs_printf *directive, const st
 		return 0;
 	}
 
-	char *target = xreadlinkat(ftwbuf->at_fd, ftwbuf->at_path, 0);
+	const struct bfs_stat *statbuf = bftw_cached_stat(ftwbuf, BFS_STAT_NOFOLLOW);
+	size_t len = statbuf ? statbuf->size : 0;
+
+	char *target = xreadlinkat(ftwbuf->at_fd, ftwbuf->at_path, len);
 	if (!target) {
 		return -1;
 	}